Two common examples of conventional convertible beds are folding frame sofa beds and futons. Folding frame sofa beds typically consist of a metal frame having several sub-frames connected by hinges about which the sub-frames can rotate. Converting the sofa bed between the sofa state and the bed state requires rotating the sub-frames relative to one another to fold or unfold the frame, often with the aid of a lever arrangement. For example, a prior art folding frame sofa bed is described in International Publication No. WH 03/049579 to Comodo Italia SRL.
There are several inconvenient aspects of this design. Firstly, the frame is heavy, particularly when combined with the padding for the sofa seat and mattress. As a result, rotating portions of the frame to convert the sofa bed is a tiring and difficult operation. To counteract this problem, lever arrangements have been developed to reduce the force required to move the frame. However, such arrangements increase the complexity of the sofa bed and the number of moving parts in it, which leads to an increase in the cost of the bed and a decrease in the reliability of the mechanism. Furthermore, since converting the bed involves temporarily lifting part of the heavy frame into an unsupported position, there is a risk that the user may be injured if the frame falls suddenly, either due to carelessness or a fault in the frame.
Futons are generally simpler in design than folding frame sofa beds and typically consist of a wooden frame having arm sections, a back section and a seat section. The back and seat sections are mounted between the arm sections on movable joints in such a way that they can both slide horizontally and rotate between a sofa position in which the back section is upright and the seat section is at an angle, and a bed position in which both sections are horizontal. Typically a futon has a single piece of padding functioning as both cushion and mattress, which must be manually rearranged when the futon is converted between the sofa and bed states. One such futon is disclosed in U.S. Pat. No. 6,715,166 to Grossman et al.
In one common design, the back section is connected to the arm sections by plastic or metal pegs which are free to move in grooves in the arm sections. The seat section of the futon is hinged on the bottom edge of the back section in such a way that it is free to rotate in a vertical plane.
As in the case of the folding frame sofa bed, the frame and mattress of the futon are heavy and bulky objects, and the process of converting the futon is difficult. Care must be exercised in pulling the seat forward, the first step of conversion between the sofa state and the bed state, to avoid the back section suddenly falling into its bed position under its own weight, which can lead to breakage or injury. Furthermore, the need for multiple joints increases the complexity and cost of the futon. The joints formed by the pegs and the grooves in the wooden arm sections are subjected to large stresses during conversion, which can result in damage to the wood,
Prior art convertible beds can only be converted into one bed, either a single or a double bed depending on the particular design.